Polyaxial bone anchoring device with enlarged pivot angle

ABSTRACT

A polyaxial bone anchoring device includes a receiving part configured to be pivotably connected to a head of an anchoring element, the receiving part having a channel for receiving a rod and an accommodation space having an opening for accommodating the head, and a sleeve-like insert piece having a sleeve axis and a spherical segment-shaped outer surface portion. The insert piece is configured to be positioned around a portion of the head in the receiving part and to pivot in the receiving part, and includes a first part and a separable second part configured to be connected with the first part by a connection structure configured to permit translational movement between the first part and the second part in a direction transverse to the sleeve axis, while preventing movement between the first part and the second part in a direction parallel to the sleeve axis.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.16/905,312, filed Jun. 18, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/962,763, filed Apr. 25, 2018, now U.S. Pat. No.10,729,483, which is a continuation of U.S. patent application Ser. No.14/575,827, filed Dec. 18, 2014, now U.S. Pat. No. 9,962,207, whichclaims priority to and the benefit of U.S. Provisional PatentApplication Ser. No. 61/919,566, filed Dec. 20, 2013, the contents ofwhich are hereby incorporated by reference in their entirety, and claimspriority from European Patent Application EP 13 198 637.4, filed Dec.19, 2013, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND Field

The invention relates to a polyaxial bone anchoring device with anenlarged pivot angle. The bone anchoring device includes a boneanchoring element for anchoring in a bone or a vertebra, a receivingpart for coupling the bone anchoring element to a stabilization elementsuch as a spinal rod, where the bone anchoring element is pivotable inthe receiving part and can be pivoted out of a central axis with anenlarged pivot angle. The orientation of the enlarged pivot angle may beselectable within a range of 360° around the central axis and may beautomatically achieved by pivoting the receiving part relative to thebone anchoring element. The receiving part can be mounted to the boneanchoring element in situ when the bone anchoring element has beenimplanted into the bone.

Description of Related Art

A polyaxial bone anchoring device with an enlarged pivot angle that isselectable within a range of 360° around the central axis is describedin US 2012/0136395 A1. The polyaxial bone anchoring device includes asleeve-like insert piece that is configured to be positioned around aportion of the head of the bone anchoring element and to pivot in thereceiving part. When the head, the insert piece and a pressure memberare arranged in the receiving part, the insert piece is tiltable withrespect to the longitudinal axis of the receiving part and with respectto a longitudinal axis of the anchoring element, and the anchoringelement and the insert piece can be locked at respective angles relativeto the longitudinal axis of the receiving part by exerting pressure withthe pressure member onto the head.

U.S. Pat. No. 7,625,396 B2 describes a polyaxial bone screw assemblythat includes a threaded shank body having an upper capture structure, ahead and a multi-piece retainer articulation structure. The head has aU-shaped cradle defining a channel for receiving a spinal fixation orstabilization longitudinal connection member. The geometry of theretainer structure pieces corresponds and cooperates with the externalgeometry of the capture structure to frictionally envelop the retainerstructure between the capture structure and an internal surface defininga cavity of the head. The retainer structure includes a substantiallyspherical surface that mates with the internal surface of the head,providing a ball joint, enabling the head to be disposed at an anglerelative to the shank body. Typically, the head and the retainerstructure are assembled on the shank before implanting the shank bodyinto the vertebra.

SUMMARY

It is an object of the invention to provide an improved polyaxial boneanchoring device with enlarged pivot angle that provides a very lowinsertion force of the bone anchoring element into the receiving partand more flexibility in use.

The polyaxial bone anchoring device according to embodiments of thepresent invention permits to mount the receiving part that may bepre-assembled with a pressure member and a sleeve-like insert piece ontoa bone anchoring element that has already been inserted into a bone orinto a vertebra. Such an “in situ” assembly of the polyaxial boneanchoring device permits a surgeon to more easily insert the boneanchoring element into the bone, especially in areas having a specificgeometry or reduced available space.

Because the polyaxial bone anchoring device according to the embodimentsis a bottom loading type polyaxial bone anchoring device, it opens avariety of possibilities of combining a specific bone anchoring elementwith a receiving part on demand prior to surgery. The bone anchoringdevice can be provided by the manufacturer as a pre-assembled receivingpart with the pressure member and the sleeve-like insert piece, andseparate therefrom, screw shanks. The polyaxial bone anchoring devicecan be assembled anywhere by anybody, in particular, by a surgeon or byany personnel assisting the surgeon before or during surgery. Variousshanks with different diameter, thread form, length or other featurescan be combined with the receiving part according to the actual clinicalrequirements in a particular clinical situation. This gives the surgeona substantial choice of implants and reduces the implant setconfiguration.

By the modularity, the costs of stock-holding can be lowered.

The sleeve-like insert piece provides for an enlarged pivot angle thatmay be equal to or greater than 45° measured from a straight position.This renders the bone anchoring device particularly suitable for theapplication of lateral mass fixation, for example, in the cervicalspine. The enlarged pivot angle can be adjusted to be at any orientationwithin 360° around the central axis by self-alignment of the sleeve-likeinsert piece when the receiving part is pivoted relative to the boneanchoring element.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from thedescription of the embodiments by means of the accompanying drawings. Inthe drawings:

FIG. 1 shows a perspective exploded view of a polyaxial bone anchoringdevice according to a first embodiment;

FIG. 2 shows a perspective view of the polyaxial bone anchoring deviceof FIG. 1 in an assembled state;

FIG. 3 shows a perspective view from the top of a receiving part of thepolyaxial bone anchoring device of FIGS. 1 and 2 ;

FIG. 4 shows a perspective view from the bottom of the receiving part ofFIG. 3 ;

FIG. 5 shows a top view of the receiving part of FIGS. 3 and 4 ;

FIG. 6 shows a cross-sectional view of the receiving part of FIGS. 3 to5 along line A-A in FIG. 5 ;

FIG. 7 shows a perspective view from the top of a pressure member of thepolyaxial bone anchoring device of FIGS. 1 and 2 ;

FIG. 8 shows a perspective view from the bottom of the pressure memberof FIG. 7 ;

FIG. 9 shows a top view of the pressure member of FIGS. 7 and 8 ;

FIG. 10 shows a cross-sectional view of the pressure member of FIGS. 7to 9 along line B-B in FIG. 9 ;

FIG. 11 shows a perspective exploded view from the top of a sleeve-likeinsert piece of the polyaxial bone anchoring device of FIGS. 1 and 2 ;

FIG. 12 shows a perspective view from the top of a first part of thesleeve-like insert piece of FIG. 11 ;

FIG. 13 shows a perspective view from the bottom of the first part ofthe sleeve-like insert piece of FIGS. 11 and 12 ;

FIG. 14 shows a top view of the first part of the sleeve-like insertpiece of FIGS. 11 to 13 ;

FIG. 15 shows a cross-sectional view of the first part of thesleeve-like insert piece of FIGS. 11 to 14 along line D-D in FIG. 14 ;

FIG. 16 shows a perspective view from the top of a second part of thesleeve-like insert piece of FIG. 11 ;

FIG. 17 shows a perspective view from the bottom of the second part ofthe sleeve-like insert piece of FIG. 16 ;

FIG. 18 shows a top view of the second part of the sleeve-like insertpiece of FIGS. 16 and 17 ;

FIG. 19 shows a cross-sectional view of the second part of thesleeve-like insert piece of FIGS. 16 to 18 along line F-F in FIG. 18 ;

FIG. 20 shows a perspective exploded view of a second embodiment of asleeve-like insert piece of a polyaxial bone anchoring device;

FIGS. 21 to 23 show cross-sectional views of steps of assembling thereceiving part and the sleeve-like insert piece according the firstembodiment of the polyaxial bone anchoring device;

FIGS. 24 to 27 show cross-sectional views of steps of mounting thereceiving part that has been pre-assembled with the sleeve-like insertpiece and the pressure member described before onto a bone anchoringelement that has been inserted into a bone;

FIG. 28 shows a cross-sectional view of a final step of mounting thereceiving part pre-assembled with the pressure member and thesleeve-like insert piece onto a bone anchoring element inserted into abone or a vertebra; and

FIG. 29 shows a cross-sectional view of a pivoted position of thereceiving part with the sleeve-like insert piece and the pressure memberand an inserted and fixed rod relative to the bone anchoring elementthat has been implanted into the bone or a vertebra.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2 , a polyaxial bone anchoring device accordingto a first embodiment includes a bone anchoring element 1 in the formof, for example, a bone screw having a threaded shank 2 and a head 3.The head 3 typically has a spherically-shaped outer surface portion 3 aand a recess 3 b at its free end for engagement with a driver or tool.The head 3 is configured to be held in a receiving part 4 that couplesthe bone anchoring element 1 to a stabilization rod 100. In thereceiving part 4, a sleeve-like insert piece 5 providing a seat for thehead 3 of the bone anchoring element 1 and a pressure member 6 forexerting pressure onto the head 3 can be arranged. Furthermore, afixation element in the form of, for example, a fixation screw 7 may beprovided for securing and fixing the rod 100 in or relative to thereceiving part 4.

The receiving part 4 has a first end or top end 4 a and a second end orbottom end 4 b, an axis C defining a central axis of the polyaxial boneanchoring device, and a coaxial bore 41 extending from the top end 4 ain a direction toward the bottom end 4 b. Adjacent to the top end 4 a, asubstantially U-shaped recess 42 is provided that forms a channel forreceiving the rod 100. By means of the recess 42, two free legs areformed which are each provided with an internal thread 43 thatcooperates with the fixation screw 7.

As shown in more detail in FIGS. 3 to 6 , the coaxial bore 41 opens intoan accommodation space 44 provided in a lower part of the receiving part4. The accommodation space 44 has a lower opening 45 at the bottom end 4b of the receiving part 4. The accommodation space 44 further includesan upper section 44 a adjacent to the coaxial bore 41 that hassubstantially the shape of a hollow spherical segment with an innerdiameter Di that is sized so as to allow the sleeve-like insert piece 5to expand therein in a direction transverse to the central axis C and tolimit the expansion. Further, the accommodation space 44 includes asecond section 44 b between the first section 44 a and the lower opening45 that also has the shape of a hollow spherical segment with a largestinner diameter being at the upper end of the second section 44 b.Adjacent to the bottom end 4 b, a third section 44 c is provided thatwidens substantially in a conical shape toward the bottom end 4 b toprovide space for pivoting of the shank 2. An inner diameter of thecoaxial bore 41 is smaller than an inner diameter of the first section44 a of the accommodation space so that an upper end surface 46 of theaccommodation space 44 provides an abutment or stop for stopping thesleeve-like insert piece 5 when moving it toward the top end 4 a. By thesecond section 44 b of the accommodation space 44, a seat for thesleeve-like insert piece 5 is provided, such that the seat and thesleeve-like insert piece 5 form a ball and socket joint. It should benoted that the seat can also be tapered, or can have various othershapes that can be used to realize a ball and socket joint. A lower endof the second section or seat 44 b in a direction towards the bottom end4 b has a smaller diameter than a largest outer diameter Do of thesleeve-like insert piece 5, so that the sleeve-like insert piece 5cannot fall through the lower opening 45 (see FIG. 28 ).

It shall be further noted that an inner diameter of the coaxial bore 41does not need to be constant between the top end 4 a and theaccommodation space 44. The coaxial bore 41 may have different portionswith different diameters.

A transverse pin hole 47 extends from an outer surface of one of thelegs into the coaxial bore 41. The pin hole 47 may serve for receiving apin 8, shown in FIG. 1 , therein.

Referring more in detail to FIGS. 7 to 10 , the pressure member 6 issubstantially cylindrical with an outer diameter that allows it to movewithin the coaxial bore 41 and the accommodation space 44 of thereceiving part 4. The pressure member 6 has an upper end 6 a and a loweredge 6 b. Adjacent to its lower edge 6 b, a spherical recess 61 with aspherical shape that matches the spherical shape of the outer sphericalsurface portion 3 a of the head 3 is provided.

At the upper end 6 a, the pressure member 6 has a cylindrical recess 62for receiving the rod 100 therein. Furthermore, the pressure member 6has a coaxial bore 63 for allowing access to the head 3 with a tool. Thecoaxial bore 63 is also configured to allow a portion of the head 3 toextend therethrough when the bone anchoring element 1 is in a pivotedcondition, as shown, for example, in FIG. 29 . A height of the pressuremember 6 in an axial direction along the central axis C is such thatwhen the fixation screw 7 is tightened, the fixation screw 7 pressesonto the rod 100, which then presses onto the pressure member 6, whichin turn acts onto the head 3 of the bone anchoring element 1.

At an outer surface of the pressure member 6, arranged centrally in atleast one of the legs provided by the cylindrical recess 62, an elongaterecess 64 is provided that extends in a direction parallel to thecentral axis. The recess 64 does not extend fully through the wall ofthe pressure member 6 and therefore forms an elongate groove. The upperand lower short sides 64 a, 64 b of the recess 64 are rounded. A widthof the elongate recess 64 in a direction transverse to the central axisC is such that the recess 64 may receive and guide a front portion ofthe pin 8, shown in FIG. 1 , therein. The pin 8, which may be acylindrical shaped pin, is configured to extend through the pin hole 47in the receiving part 4 into the elongate recess 64. A function of theelongate recess 64 is to maintain an aligned position of the pressuremember 6 relative to the receiving part 4 such that the recesses 62 ofthe pressure member 6 and the recess 42 of the receiving part 4 arealigned for receiving the rod 100. Furthermore, the elongate recess 64provides at its upper short side 64 a an abutment for the pin 8 when thepressure member 6 is inserted into the receiving part 4 and moveddownward. The lower short side 64 b serves as a stop for the pin 8 whenthe head 3 of the anchoring element 1 is inserted into the accommodationspace 44 and pushes against the spherical recess 61 of the pressuremember 6, thereby moving the pressure member 6 upwards, as shown inFIGS. 26 and 27 .

At a distance from the lower edge 6 b, the pressure member 6 includes acircumferentially extending groove 65. A depth of the groove 65 may besubstantially the same as a depth of the elongate recess 64. A height ofthe groove 65 in the direction parallel to the central axis is such thatthe groove 65 extends from the axial position of the spherical recess 61up to the axial position of the bore 63. The function of the groove 65is to reduce the size of an outer diameter of the pressure member 6 toallow a portion of the sleeve-like insert piece 5 to extend into thegroove 65 when the receiving part 4 with the pressure member 6 and thesleeve-like insert piece 5 is tilted with respect to the longitudinalaxis L of the bone anchoring element 1, as can be seen in FIG. 29 .

Referring to FIG. 11 , the sleeve-like insert piece 5 includes twoparts, a left part or first part 510 and a right part or second part520. Each part has an upper edge 5 a and a lower edge 5 b. The firstpart 510 and the second part 520 are connected by a connection structure51 described below. Both the first part 510 and the second part 520 formhalves of a sleeve or a ring that has a sleeve axis S.

Referring to FIGS. 12 to 19 in more detail, each of the first part 510and the second part 520 has a central inner portion 52 that is hollowand spherical segment-shaped with a radius corresponding to a radius ofthe spherically shaped outer surface portion 3 a of the head 3 of thebone anchoring element 1. The outer surfaces 53 of the first part 510and the second part 520 are spherical segment-shaped, so that when thefirst part 510 and the second part 520 are mounted together, thesleeve-like insert piece 5 has an outer contour of a segment of asphere. The outer surface 53 is sized and shaped to cooperate with theinner surface of the seat 44 b of the accommodation space 44 of thereceiving part 4, such that the sleeve-like insert piece 5 can beslidably and pivotably held in the seat 44 b of the accommodation space.Center points of the inner spherical surface 52 and the outer sphericalsurface 53 may be the same. In some embodiments, the center point of theinner spherical surface portion 52 may instead be offset from the centerpoint of the outer spherical surface portion 53 in a direction towardthe lower edge 5 b to further increase a maximum pivot angle of the boneanchoring element 1 relative to the receiving part 4.

When the sleeve-like insert piece 5 rests in the seat 44 b such that itssleeve axis S is coaxial with the central axis C of the receiving part4, the lower edge 5 b projects out of the lower opening 45 (see FIG. 28). When the sleeve-like insert piece 5 is pivoted or angled in thereceiving part 4, as shown for example in FIG. 29 , at least a portionof the lower edge 5 b still projects out of the lower opening 45.

A lower end of the central portion 52 forms a shoulder 52 a. An innerdiameter of the shoulder 52 a is smaller than a largest outer diameterof the spherical head 3, so that the head 3 can rotate and pivot in thecentral spherical portion 52 of the sleeve-like insert piece 5, similarto a ball and socket joint. Between the shoulder 52 a and the lower edge5 b, a tapered portion 54 is provided that conically widens outward toallow angulation of the bone anchoring element 1 until the shank 2 comesinto contact with the lower edge 5 b. A coaxial recess 55 extends fromthe upper edge 5 a into the sleeve-like insert piece 5 up to the innercentral spherical portion 52. An inner diameter of the cylindricalrecess 55 is greater than an inner diameter of the central sphericalportion 52 so that a space is provided for the lower portion of thepressure member 6. Hence, an inner diameter of the cylindrical recess 55is greater than an outer diameter of the lower portion of the pressuremember 6. Moreover, the size of the cylindrical recess 55 is such that,when the bone anchoring element 1 assumes a maximum pivot angle withrespect to the receiving part 4, the pressure member 6 may not block thesleeve-like insert piece 5 from reaching the maximum pivot angle, asshown in FIG. 29 .

The first part 510 and the second part 520 each have two free endsurfaces 510 a, 510 b, 520 a, 520 b that extend in a plane containingthe sleeve axis S. As can be seen in FIG. 11 , the first free endsurface 510 a of the first part 510 faces the first free end surface 520a of the second part 520 and the second free end surface 510 b of thefirst part 510 faces the second free end surface 520 b of the secondpart 520.

Each end surface 510 a, 510 b of the first part 510 has two maleconnection elements in the form of pins 56 that are spaced from eachother in a vertical direction and that project in a directionperpendicular to the sleeve axis S. The pins 56 may be shaped and sizedidentically. On the opposing free end surfaces 520 a, 520 b arecorresponding female connection elements in the form of recesses or pinholes 57 that match, regarding their position and shape, the positionand shape of the pins 56, so that when the first part 510 and the secondpart 520 are mounted together, the pins 56 engage the corresponding pinholes 57 to generate a form-fit connection. The shape of the pins 56 andthe pin holes 57 may be cylindrical, and as a result thereof, when thefirst part 510 and the second part 520 are moved relative to each other,the movement may be in a direction transverse to the sleeve axis S. Inaddition, the pins 56 contact the inner walls of the pin holes 57 alongsome length of the pins 56 so that a tilting motion of the first part510 and relative to the second part 520 is inhibited. When thesleeve-like insert piece 5 is in the receiving part 4, the path ofmovement of the two parts 510, 520 relative to each other may be limitedon the one hand by the abutment of the free end surfaces 510 a, 520 aand 510 b, 520 b with one another, when the parts are assembled to formthe sleeve-like insert piece 5, and on the other hand by the inner wallsof the first section 44 a of the accommodation space 44 in which thesleeve-like insert piece 5 can expand. Preferably, a maximum innerdiameter of the first section 44 a of the accommodation space 44 isslightly smaller than a maximum outer diameter Do of the sleeve-likeinsert piece 5 when assembled plus the length of the pins 56, so thatthe two parts 510, 520 cannot fully separate in the accommodation space44.

It shall be noted that while two pins and corresponding pin holes areshown, only one pin on each surface may be sufficient. In someembodiments, more than two pins may be contemplated. In addition,various modifications may be envisaged, such as providing a first pin onthe first part 510 and a pin hole on the second part 520 and a secondpin on the second part 520 and the pin hole on the first part 510.

A modified embodiment of the sleeve-like insert piece 5′ is shown inFIG. 20 . The sleeve-like insert piece 5′ differs in the design of theconnection structure 51′ from the sleeve-like insert piece 5 of thefirst embodiment. All other parts and portions that are the same orsimilar have the same reference numerals, and the descriptions thereofwill not be repeated.

The sleeve-like insert piece 5′ has a connection structure 51′ that hasmale connection elements in the form of pins 56′ with a rectangularstructure instead of cylindrical pins. The second part 520′ has at eachof its free end surfaces 520 a, 520 b only one pin 56′ with arectangular cross-section, wherein the long sides of the rectangleextend substantially parallel to the sleeve axis S. On the free endsurfaces 510 a, 510 b of the first part 510′ there are correspondingfemale connection elements in the form of recesses 57′ having a size andshape that matches the shape of the pins 56′. The recesses 57′ are opentowards the outer surface 53.

It shall be contemplated that any connection structure that permitsmoving of the two parts 510, 520, 510′, 520′ apart, while simultaneouslymaintaining the orientation of the two parts with respect to each other,can be used.

The bone anchoring device, as a whole or in part, may be made of abio-compatible material, such as a bio-compatible metal, for exampletitanium or stainless steel, of a bio-compatible alloy, such as aNiTi-alloy, for example Nitinol, or of bio-compatible plastic materials,such as, for example, polyether ether ketone (PEEK), or of abio-compatible ceramic material.

Referring to FIGS. 21 to 23 , steps of assembling the receiving part 4,the sleeve-like insert piece 5, and the pressure member 6 together areexplained with respect to the first embodiment of the sleeve like insertpiece 5. The same steps are carried out, however, when the modifiedsleeve-like insert piece 5′ of the second embodiment is used.

First, the two parts 510, 520 are put together such that the pins 56engage the recesses 57 and the free end surfaces 510 a, 520 a and 510 b,520 b abut each other to form the sleeve-like insert piece 5. Then, asshown in FIG. 21 , the sleeve-like insert piece 5 is tilted by 90° andinserted into the receiving part 4 at the position of the U-shapedrecess 52. The sleeve-like insert piece 5 is moved downward (asillustrated) toward the bottom end 4 b of the receiving part 4. Asdepicted in FIG. 22 , when the sleeve-like insert piece 5 hassufficiently entered the accommodation space 44, it is tilted and movedfurther downward until it is seated with its spherical outer surface 53in the seat 44 b of the accommodation space 44 (see FIG. 23 ). Thesleeve-like insert piece 5 cannot escape through the lower opening 45,because an inner diameter of the lowermost portion of the seat 44 b issmaller than the maximum outer diameter Do of the sleeve-like insertpiece 5. The lower edge 5 b projects outward from the bottom end 4 b ofthe receiving part 4. As further shown in FIG. 23 , the pressure member6 is inserted into the receiving part 4 through the coaxial bore 41 sothat its lower edge 6 b extends into the cylindrical recess 55 of thesleeve-like insert piece 5. Thereafter, the pin 8 is inserted into thetransverse pin hole 47 of the receiving part 4 such that its frontsurface facing the pressure member 6 extends into the elongate recess64. When the pin 8 abuts against the upper side 64 a of the recess 64,the pressure member 6 is prevented from moving any further downward.Simultaneously, the pressure member 6 is held by the pin 8 such that itscylindrical recess 62 is aligned with the U-shaped recess 42 of thereceiving part 4. In the arrangement shown in FIG. 23 , the sleeve-likeinsert piece 5 is movable in an axial direction relative to thereceiving part 4 and is slidably pivotable in the seat 44 b.

The use of the bone anchoring device is explained by referring to FIGS.24 to 27 . First, the bone anchoring element 1 is inserted into a bonepart or a vertebra, for example, into the pedicle of a vertebra, suchthat the head 3 extends above the bone surface 200 as depicted in FIG.24 . The receiving part 4 that is pre-assembled with the sleeve-likeinsert piece 5 and the pressure member 6 is not yet mounted to the boneanchoring element. Hence, the bone anchoring 1 element can be moreeasily inserted, which may be advantageous in cases where the insertionlocations of the bone anchoring element 1 are difficult to reach or incases where the insertion location has small or limited available space.As further depicted in FIG. 24 , the receiving part 4 may be movedtowards the bone anchoring element 1 using, for example, an instrument(not shown). Next, as shown in FIG. 25 , through further downwardmovement of the receiving part 4, the head 3 abuts with its sphericalouter surface portion 3 a against the shoulder 52 a of the sleeve-likeinsert piece 5 and enters through the lower opening 45 of the receivingpart 4. This moves the sleeve-like insert piece 5 out of the seat 44 binto the first section 44 a of the accommodation space 44 as depicted bythe vertical arrows beneath the bottom end 4 b of the receiving part 4in FIG. 25 .

Further upward movement of the sleeve-like insert piece 5 into the firstsection 44 a of the accommodation space, through for example, pushingvia the head 3 of the bone anchoring element 1 moves the sleeve-likeinsert piece 5 to a position where separation of the parts 510, 520 ismore easily facilitated, and once in that position, the first part 510and the second part 520 of the sleeve-like insert piece 5 beginseparating in a direction transverse to the central axis C due to theforce applied by the spherical shape of the head 3, as indicated by thetransverse arrows depicted in FIG. 26 . The two parts 510, 520 can moveapart, wherein the movement is limited by the inner wall of the firstsection 44 a of the accommodation space. The movement is guided orrestricted by the pins 56 which are still positioned in the respectiverecesses 57. When the two parts 510, 520 move away from each other, thehead 3 is able to enter between the two parts 510, 520 until the head 3enters the cylindrical recess 55 and abuts against the spherical recess61 of the pressure member 6, as also shown in FIG. 26 . The insertion ofthe bone anchoring element 1 into the receiving part 4 thereforerequires a very low insertion force.

When the head 3 further presses against the spherical recess 61 of thepressure member 6, the pressure member 6 moves further upward relativeto the first end 4 a of the receiving part 4 until the pin 8 abutsagainst the lower end 64 b of the elongate recess 64. In this condition,the pressure member 6 is prevented from escaping through the top end 4 aof the receiving part 4 by the pin 8. As shown in FIG. 27 , when thepressure member 6 and the head 3 are in their uppermost positionrelative to the receiving part 4, the head 3 no longer exerts pressureonto the two parts 510, 520 of the sleeve-like insert piece 5, so thatthe two parts 510, 520 can move back towards each other and downwarduntil the sleeve-like insert piece 5 is seated again in the seat 44 b.During this downward movement, the two parts 510, 520 are slidablyguided by the connection structure 51 realized by the pins 56 and therecesses 57.

Finally, as depicted in FIG. 28 , the receiving part 4 is pulledslightly upward (as illustrated), so that the head 3 of the boneanchoring element 1 is drawn into the seat 52 of the sleeve-like insertpiece 5. In this pre-locking configuration, the head 3 is prevented frombeing pulled out from the receiving part 4 because the head 3 is seatedin the central portion 52 of the sleeve-like insert piece 5 and thesleeve-like insert piece 5 is seated in the seat 44 b of the receivingpart 4, and it cannot fall through the lower opening 45.

It shall be noted that the size of the pressure member 6, the elongaterecess 64 and the position of the pin 8 can be designed such that in thecondition shown in FIG. 28 , the pressure element exerts a slightpreload onto the head 3, so that the head 3 is frictionally held betweenthe sleeve-like insert piece 5 and the pressure member 6. By such means,the receiving part 4 can be maintained at a temporary angular positionwith respect to the bone anchoring element 1 before the angular positionis finally locked.

After several bone anchoring devices are implanted into bone parts oradjacent vertebrae, the receiving parts 4 are tilted, as shown forexample, in FIG. 29 , to align their channels for receiving thestabilization rod 100. The sleeve-like insert piece 5 is rotatable andpivotable in the receiving part 4, while the receiving part 4 and thesleeve-like insert piece 5 are both rotatable and pivotable with respectto the head 3 of the bone anchoring element 1. The sleeve-like insertpiece 5 provides for an enlarged range of angulation compared to boneanchoring devices where the head 3 is directly received in the receivingpart 4, because the insert piece 5 increases the distance between theshank 2 of the bone anchoring element 1 and the abutment provided by theedge of the lower opening 45 at the bottom end 4 b.

As depicted in FIG. 29 , the shank 2 pushes the insert piece 5 until theshank 2 abuts against the wall of the third section 44 c of theaccommodation space 44. Hence, in FIG. 29 , the receiving part 4 ispivoted at a maximum pivot angle with respect to the bone anchoringelement 1. The maximum pivot angle that can be achieved depends on thedimensions of the sleeve-like insert piece 5, the receiving part 4, andthe bone anchoring element 1, but is typically equal to or greater than45° measured from a straight or zero angle position between thereceiving part 4 and the bone anchoring element 1.

Because the sleeve-like insert piece 5 is rotatable and pivotable withinthe receiving part 4, the enlarged range of angulation can be achievedat any position of the receiving part 4 with respect to the boneanchoring element 1, for all 360° around the central axis C of thereceiving part 4.

While in FIG. 29 an example is shown in which pivoting is carried out ina plane perpendicular to the rod axis of rod 100, it should be noted,that pivoting can be carried out in any other direction within 360°around the central axis C of the receiving part 4.

Finally, the rod 100 is inserted and the fixation screw 7 is tightenedto press the pressure member 6 onto the head 3 to lock the head 3 andthe sleeve-like insert piece 5 simultaneously.

It shall be noted that the bone anchoring device can also be used in amanner where the receiving part 4, the sleeve-like insert piece 5, thepressure member 6 and the bone anchoring element 1 are pre-assembled,and thereafter the bone anchoring element 1 is inserted into the bone.

Further modifications of the embodiments may also be contemplated. Forexample, for the bone anchoring element, various different kinds ofanchoring elements can be used and combined with the receiving part 4.These anchoring elements may be, for example, screws with differentlengths, screws with different diameters, cannulated screws, screws withdifferent thread forms, nails, hooks, etc. For some anchoring elements,the head and the shank may also be separate parts that are connectableto each other.

Other possible modifications of the receiving part may include, forexample, instead of the U-shaped recess being perpendicular to thecentral axis, a recess for the rod may be inclined, open to the side, orin the form of a closed channel. Other kinds of locking devicesincluding outer nuts, outer caps, bayonet locking devices, or others arealso possible. In particular, a two part locking device that includes afirst locking element that exerts pressure via the pressure member 6only onto the head and a second locking element that exerts pressureonly onto the rod to lock the head 3 and the rod independently may alsobe used. In some embodiments, the inner surface portion of the pressuremember that contacts the head 3 may not necessarily bespherically-shaped. The inner surface portion may have any other shapethat is suitable to exert pressure onto the head.

Instead of the pin 8 cooperating with the elongate recess 64 provided atthe pressure element, other retaining mechanisms can be used forretaining the pressure member 6 in alignment with the receiving part 4and to inhibit the pressure member 6 from moving out through the top endof the receiving part 4. For example, two retaining members, one on eachside of the channel of the receiving part, may be provided.

With regard to the sleeve-like insert piece, exemplary embodiments withtwo parts are shown. However, it may be contemplated that more than twoparts are connected through various connection structures to form thesleeve-like insert piece.

The head of the bone anchoring element needs not to be rotationallysymmetric. For example, the head may have two opposite flat surfaceportions between two spherically-shaped outer surface portions, so as toachieve pivoting in only one plane.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

1. A polyaxial bone anchoring device comprising: an anchoring elementhaving a shank for anchoring in the bone and a head, the head having aspherically-shaped outer surface portion; a receiving part configured tobe pivotably connected to the head, the receiving part having a top endand a bottom end, a central axis extending through the top end and thebottom end, a transverse channel for receiving a rod and anaccommodation space for accommodating the head, the accommodation spacehaving a lower opening at the bottom end; and a sleeve-like insert piecehaving a sleeve axis and configured to be positioned around a portion ofthe head, the insert piece comprising a spherically-shaped outer surfaceportion. 2-5. (canceled)
 6. The polyaxial bone anchoring device of claim1, wherein the sleeve-like insert piece has an inner spherically-shapedsurface portion that forms a seat for the head. 7-12. (canceled)
 13. Thepolyaxial bone anchoring device of claim 1, wherein a lower edge of thesleeve-like insert piece extends through the lower opening when thesleeve-like insert piece is seated in the receiving part in a positionin which its sleeve axis is coaxial with the central axis. 14-16.(canceled)
 17. The polyaxial bone anchoring device of claim 1, whereinthe receiving part has a passage extending from the top end into theaccommodation space and wherein the inner diameter of the passage at thetop end is smaller than the largest outer diameter of the sleeve-likeinsert piece.
 18. The polyaxial bone anchoring device of claim 6,wherein the outer spherically-shaped surface portion and the innerspherically-shaped surface portion of the sleeve-like insert piece havethe same center point.